Render 2 at Once - Faster than One?
You can start multiple jobs at the same time, but they don't render any faster.
In my experience, one will grab most of the resources and the second job will go along at a snails pace until the first finishes.  You also have to worry more about going over the total amount of resources in your machine.  The one advantage is you can start them both and go to bed without having to worry about it.
If you want unattended batch rendering there are services for it, or blender can be set to start a render through the command line; you could create a batch file for multiple jobs.